The present invention relates in general to wafer cleaning, and more particularly to methods of spin-on wafer cleaning.
Semiconductor process technologies, such as deposition, etching and polishing, usually generate particles. If the particles are not removed, they can seriously impact product yield. For example, the particles may impede current flow and degrade performance of the product, or cause surface roughness affecting subsequent processing. Also, particles dropping from a wafer and into equipment can cause damage to and shorten the lifespan of the equipment.
In a scrubber, a wafer to be cleaned is fixed on a vacuum chuck. De-ionized water is sprayed on the spinning wafer surface to remove particles, referred to as spin-on wafer cleaning.
Wafer spin in a conventional spin-on wafer cleaning process creates electrostatic charge generation friction between the wafer and de-ionized water or air. Since de-ionized water is not conductive, the accumulated electrostatic charge generates a voltage on the wafer surface. The electrostatic charge on the wafer may cause a shift in the electrical characteristics of a semiconductor device and induce low yield.
In one method commonly used in spin-on wafer cleaning to reduce voltage build up on the semiconductor wafer, chemicals, such as carbon dioxide, are added to the de-ionized water to increase conductivity, thereby dispersing the generated charge. However, it can be inconvenient to prepare such cleaning liquid and chemicals remaining on the wafer surface after cleaning may affect the electrical characteristics of the semiconductor device.